Jet aircraft are large, but not compared with the ocean. The weeks-long search for some physical sign of Malaysia Airlines Flight 370 is not something we should wonder at, considering the frontier nature of our blue planet.

The 29% of our planet that is land is inhabited by more than 7 billion of our species, at least a few of whom would have reported a crash or hijacked aircraft. By contrast, the ocean that covers 71% of the Earth's surface and 97% of its living habitat rarely has more than a few million people on or about its surface. These include commercial mariners, fishermen, cruise ship passengers, sailors aboard the world's military fleets, offshore oil and gas workers, research scientists and the odd sea gypsy.

One reason we've not colonized the ocean, as science-fiction writers (and at least one senator, the late Claiborne Pell, of Rhode Island) once imagined, is that the ocean is a far rougher and more difficult wilderness than any encountered by terrestrial explorers, or even astronauts traveling in the consistent vacuum of space, with its occasional meteorites and space junk to avoid.

The sea pummels us with an unbreathable and corrosive liquid medium; altered visual and acoustic characteristics; changing temperatures, depths and pressures; upwellings; tides; currents; gyres; obscuring marine layers; sudden storms and giant rouge waves; and life forms than can sting, poison or bite.

Even accounting for more than 70 years of classified military hydrographic surveys, we've still mapped less than 10% of the ocean with the resolution we've used to map all of the moon, Mars or even several moons of Jupiter.

Obviously, our ability to search for a missing aircraft at sea has come a long way since Amelia Earhart disappeared while trying to cross the Pacific in 1937. But the patched-together satellite data and electronic-signals processing that has so far pointed the Flight 370 search to an area 1,800 miles from Perth, Australia, is no more than a crisis-mode, jury-rigged, extraordinary effort. Consider this: If you're a drug smuggler and you enter U.S. coastal waters in a speedboat at night, and then go dead in the water during the day, with a blue tarp thrown over your vessel, odds are that you'll successfully deliver your contraband.

Our investment in ocean exploration, monitoring and law enforcement efforts is at a 20-year low in the United States and not much better elsewhere. Our chances of quickly finding the missing Malaysian flight would have been improved if we had invested more money and effort on our planet's last great commons, with observational tools such as in-situ labs and wired benthic observatories, remote and autonomous underwater vehicles and gliders, forward-looking infrared cameras and multi-beam shipboard, airborne (and space-deployed) scanning systems, and other smart but woefully underfunded sea technologies.

The fact remains that while hundreds of people have gone into space, only three humans have ventured to the lowest point on our planet seven miles down in the Mariana Trench, and the latest of these — filmmaker explorer engineer James Cameron — had to self-fund his 2012 mission.

Meanwhile, when it comes to exploring the cosmos, NASA — even in its diminished state — outspends NOAA's ocean exploration program roughly 1,000 to 1. Yet when we get to Mars, the first thing we seek as proof of life is water. Meanwhile, we have a whole water planet that remains a challenge we've once again discovered to be far greater than we thought.

Whatever the final resolution of the Flight 370 tragedy, that challenge is bound to become greater as our food and coastal security, marine transportation systems, even our basic ecosystem processes such as the oxygen generated by ocean plankton, are increasingly stressed through overfishing, pollution, loss of coastal habitat and ocean impacts from climate change.

Investing in the exploration and understanding of our planet's largest habitat should be a given. Perhaps that will be a lesson learned from our latest human disaster. Unfortunately, while the sea is still vast, our ability to act wisely in our own interests is often limited.

David Helvarg is executive director of Blue Frontier, a marine conservation and policy group. His latest book is "The Golden Shore: California's Love Affair With the Sea."

BEIJING — The search and rescue teams working off the west coast of Australia seeking the missing Malaysia Airlines Flight 370 discovered what oceanographers have been warning: Even the most far-flung stretches of ocean are full of garbage.

Malaysia Airlines Flight 370, carrying 239 people, disappeared on March 8, 2014. On March 24, the Malaysian prime minister announced that the flight "ended in the southern Indian Ocean" with no hope of survivors.

BEIJING -- An Australian military plane participating in the search for missing Malaysia Airlines Flight 370 on Thursday detected an underwater acoustic signal that may be from the Boeing 777’s black boxes, Australian authorities said.

BEIJING – A British submarine joined the search Wednesday for the missing Malaysia Airlines jet as Malaysian police said their probe of the 227 passengers found no personal or psychological problems or motivation to hijack or sabotage the aircraft.